Transducer circuit for simultaneous two way operation

ABSTRACT

Disclosed is a transducer circuit arrangement which allows a transducer element to be operated simultaneously in both a sending mode and a receiving mode. The transducer element forms one impedance leg of a bridge network and is in a sending mode with the signal energizing the bridge. The circuit connected between the taps of the legs of the bridge network comprise a balanced circuit means for detection of signals which the transducer develops in its receiving mode. The transducer may be a device which operates both as a speaker and as a microphone without switching between the two modes of operation. Two such transducers may be used either in series or in a parallel network to simplify the balancing of the bridge network and broaden the frequency response of the circuit.

United States Patent [191 Gschwandtner Oct. 16, 1973 [22] Filed: Feb. 22, 1972 [21] Appl. No.: 228,181

[52] US. Cl. 179/1 HF, 179/1 H [51] Int. Cl. H04m l/00 [58] Field of Search 179/1 H, 1 HF, 1 R

[56] References Cited UNITED STATES PATENTS 11/1959 Montgomery 179/1 HF 11/1958 Kaelin 179/81 B Primary Examiner-Kathleen H. Claffy Assistant Examiner-Douglas W. Olms Attorney-Roy l-l. Olson et al.

[5 7] ABSTRACT Disclosed is a transducer circuit arrangement which allows a transducer element to be operated simultaneously in both a sending mode and a receiving mode. The transducer element forms one impedance leg of a bridge network and is in a sending mode with the signal energizing the bridge. The circuit connected between the taps of the legs of the bridge network comprise a balanced circuit means for detection of signals which the transducer develops in its receiving mode. The transducer may be a device which operates both as a speaker and as a microphone without switching between the two modes of operation. Two such transducers may be used either in series or in a parallel network to simplify the balancing of the bridge network and broaden the frequency response of the circuit.

7 Claims, 5 Drawing Figures Patented Oct. 16, 1973 3,766,319

SKiNAL OUT TRANSDUCER CIRCUIT FOR SIMULTANEOUS TWO WAY OPERATION BACKGROUND OF THE INVENTION This invention relates generally to transducer circuit arrangements and more particularly to transducers which are used as speakers and microphones.

Heretofore, transducer elements have been utilized to operate both as speakers and as microphones by changing the means of energizing the device. However, the circuit path of such transducer elements has associated therewith suitable switching means to change the signal path and thus change the mode of operation of the transducer to either a speaker or a microphone. For example, in an intercom system a speaker is used at two or more locations of the system. One person speaks into one unit while depressing a talk switch to operate it as a microphone during one instance and then releases the talk switch and listens for a response from a second unit during another instance during which the transducer is used as a speaker. This requires the user to operate the talk switch on the intercom between the sending and receiving modes of operation. In many instances the intercom will always be in a receiving mode and only will transmit when the talk switch is actuated. Furthermore, when utilizing speakers in both the speaker and microphone modes of operation their impedance characteristic is dependent on the particular frequency at which they are operated and if the frequency changes, so also does the impedance.

While the preferred embodiment disclosed herein is directed to a transducer which can be used both as a speaker and as a microphone during simultaneous operation, it will be understood that other transducer elements which produce mechanical signals in one mode and electrical signals in another mode can be operated by the circuit arrangement of this invention.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a transducer circuit arrangement whereby the transducer can operate simultaneously as both a sending unit and as a receiving unit, such as a speaker and microphone, respectively.

Another object of this invention is to provide a transducer circuit arrangement whereby the balance of the bridge is maintained relatively constant over a wide range of frequencies.

Briefly, the transducer circuit arrangement of this invention includes a transducer element connected in circuit with first, second and third impedance elements or networks to form a bridge circuit therewith. The transducer element is located in one of the legs of the bridge circuit and has the same impedance as the corresponding impedance element in the other leg of the bridge circuit. Connected between the two legs of the bridge circuit at the center tie points thereof is circuit means forming the cross coupling impedance network between the legs of the bridge and which also acts as either a signal applying device to the transducer for operating in one mode or as a signal receiving circuit for receiving signals from the transducer when operating in another mode.

Many other objects, features and advantages of this invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein like reference numerals throughout the various views of the drawings are intended to designate similar elements or components.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of one form of this invention utilizing a single transducer element for simultaneous two way operation but here shows the equivalent circuit with the transducer element used as a sending unit;

FIG. 2 is an equivalent arrangement of the same circuit of FIG. 1 but shows the transducer element used as a receiving unit; I

FIG. 3 is an alternate form of the invention shown in FIG. 1 wherein a pair of similar transducer elements are used in a common leg of the bridge circuit and are used in the sending mode of operation;

FIG. 4 illustrates the equivalent circuit of FIG. 3 when used in a receiving mode of operation; and

FIG. 5 shows an alternate form of this invention wherein two transducer elements are connected in separate legs of the associated bridge circuit.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Referring now to FIG. 1 there is seen a transducer circuit arrangement constructed in accordance with the principles of this invention and is designated generally by reference numeral 10. The transducer circuit arrangement 10 includes a transducer element 11 which is connected'into a bridge network 12 to be part of one of the legs of the bridge network.

An impedance means 13 is connected in series with the transducer element 11 and forms the other component of the associated leg of the bridge. A similar impedance means 14 is connected in series with animpedance means 16 to form the other leg of the bridge, it being understood that the impedance means 13, 14 and 16 may be of any suitable configuration either discrete components or circuit networks as desired. The impedance means l3, l4 and 16 are primarily AC devices for use at audio frequencies. Connected between the center points of the two legs of thebridge is an impedance network 17 which may take the form of a differential amplifier or a two way isolation transformer to allow signals to pass from a signal source 18 into the transducer element 11 when it is used as a speakerand to receive signals from the transducer element 11 when it is used as a microphone. When the transducer element 11 is used as a microphone it is represented by a signal source 19 connected in series therewith. The signal source 19 will apply a signal to the input of the differential amplifier represented by the impedance network 17.

For a better understanding of the circuit arrangement of this invention when used as a microphone, reference is now made to FIG. 2 which shows the equivalent circuit connection. In this instance the reverse impedance of the signal source 18 is low as compared to the impedance means 13, 14 and 16, and therefore is substantially a grounded connection and is therefore eliminated from the equivalent circuit of FIG. 2. Here the with the impedance means 17 and then applied to a suitable amplifier network, not shown.

Referring now to FIG. 3 there is seen an alternate embodiment of this invention wherein a pair of transducer elements 21 and 22 are connected in series and form one leg of the bridge. Signal sources 23 and 24 represent the equivalent network when the transducer elements 21 and 22, respectively, are used as microphones. The other leg of the bridge is formed by impedance means 26 and 27 which have their tie point connected to the tie point of transducer elements 21 and 22 through an impedance network 28, which, as mentioned above with regard to the impedance network 17, can be a differential amplifier or a two way transducer network. Here the signal source 29 applies signals to the bridge circuit so that transducer elements 21 and 22 operate as speakers. In this instance, the frequency response of the speaker arrangement is increased without substantially unbalancing the bridge. While the speakers 21 and 22 can have substantially the sameimpedance characteristics their frequency characteristics can be altered by changing their mounting position relative to one another such as their position on mounting boards or within cabinets.

FIG. 4 shows the equivalent circuit of that shown in FIG. 3 when the transducer elements 21 and 22 are used as a microphone pickup. Also in this instance the reverse impedance of the signal source 29 is substantially zero as compared to the'high impedance of the impedance means 26 and 27 and the impedance network 28 and therefore is not shown in the circuit. Effectively the transducer elements 21 and 22 are connected in parallel, with one end thereof connected to ground as shown. Similarly, the impedance means 26 and 27 are connected in parallel and to ground with the impedance network 28 connected between the transducer elements 21 and 22 and the impedance means 26 and 27. An imbalance in the bridge circuit will cause 8 current to flow through the impedance network 28, as mentioned above and produce an output signal.

Referring to FIG. an alternate form of the two transducerelement circuit of FIGS. 3 and 4 is shown. Here two transducer elements 31 and 32 are connected in series with respective impedance means 33 and 34 which: form the two legs of the bridge circuit. Connected between the circuit points of their respective transducer elements and series impedance means is an impedance network 36 which may be formed of a differential amplifier or two way isolation transformer circuit as discussed above. Here the signal source 37 applies signals to the bridge circuit for operating the transducer elements 31 and 32 as speakers. However, when the transducer elements are operated as microphones an imbalance in the respective legs of the bridge will cause current to flow through the impedance network 36 and produce the appropriate output signal. In the embodiment shown in FIG. 5 the impedance and/or voltages developed within the transducer elements 31 and 32 are not equal during operation so that the necessary imbalance in the bridge circuit will occur to produce a signal within the impedance net- 4 work 36.

In all of the embodiments disclosed herein the circuit operates simultaneously as a speaker output circuit or as a microphone input circuit without the use of switching means to change between the modes of operation. While only several specific embodiments of the invention have been disclosed herein, it will be understood that other variations and modifications may be effected without departing from the spirit and scope of the novel concepts disclosed and claimed herein.

The invention is claimed as follows:

1. A transducer circuit arrangement comprising in combination, a transducer element having'a sending mode and a receiving mode, first, second, and third impedance elements, said transducer element and said first impedance element being connected together at a first intermediate circuit point to form one leg of a bridge circuit, said second and third impedance. elements being connected together at a second intermediate circuit pointto form the other leg of said bridge circuit, signal applying means connected across the ends of said legs of said bridge .circuit to operate said transducer in said sending mode, said signal applying means having a low reverse impedance to be substantially eliminated from the circuit when said transducer element is in the sending mode, and a single two-way circuit means connected between the two legs of said bridgecircuit at said first and second intermediate circuit points for receiving signals from said transducer when said transducer operates in said receiving mode and for passing signals from said signal applying means to said transducer during a sending mode to provide simultaneousv two-wayoperation of said transducer circuit.

2. The transducer circuit arrangement of claim 1 wherein said first impedance element is a second transducer element connected in series with the first transducer element.

3. The transducer circuit arrangement of claim 2 wherein said first and second transducer are substantially identical in configuration.

4. The transducer circuit arrangement of claim 2 wherein said first and second transducersoperate as speakers when in the sending mode and operate as microphones when in said receiving mode.

5. The transducer circuit arrangement of claim 1 wherein said transducer operates as a speaker when in the sending mode and operates as a microphone when ,in said receiving mode.

connected in similar portions of their associated legs of said bridge circuit, whereby the impedance of said first and second transducer elements must be different to produce a signal from said circuit means or deliver a signal to said circuit means. 

1. A transducer circuit arrangement comprising in combination, a transducer element having a sending mode and a receiving mode, first, second, and third impedance elements, said transducer element and said first impedance element being connected together at a first intermediate circuit point to form one leg of a bridge circuit, said second and third impedance elements being connected together at a second intermediate circuit point to form the other leg of said bridge circuit, signal applying means connected across the ends of said legs of said bridge circuit to operate said transducer in said sendIng mode, said signal applying means having a low reverse impedance to be substantially eliminated from the circuit when said transducer element is in the sending mode, and a single two-way circuit means connected between the two legs of said bridge circuit at said first and second intermediate circuit points for receiving signals from said transducer when said transducer operates in said receiving mode and for passing signals from said signal applying means to said transducer during a sending mode to provide simultaneous two-way operation of said transducer circuit.
 2. The transducer circuit arrangement of claim 1 wherein said first impedance element is a second transducer element connected in series with the first transducer element.
 3. The transducer circuit arrangement of claim 2 wherein said first and second transducer are substantially identical in configuration.
 4. The transducer circuit arrangement of claim 2 wherein said first and second transducers operate as speakers when in the sending mode and operate as microphones when in said receiving mode.
 5. The transducer circuit arrangement of claim 1 wherein said transducer operates as a speaker when in the sending mode and operates as a microphone when in said receiving mode.
 6. The transducer circuit arrangement of claim 1 wherein said third impedance element is a second transducer element connected in said other leg of said bridge circuit.
 7. The transducer circuit arrangement of claim 6 wherein said first and second transducer elements are connected in similar portions of their associated legs of said bridge circuit, whereby the impedance of said first and second transducer elements must be different to produce a signal from said circuit means or deliver a signal to said circuit means. 